The present invention relates generally to electrical circuit device drivers. More specifically, the present invention is directed to a feedback circuit for line load compensation and reflection reduction in free-topology module wiring configurations.
Computer systems and control systems connect to peripherals, sensors, and other electronic devices by means of various connection methods. Wired devices can be connected in various configurations, or topologies, such as linear bus, tree, star and star-wired ring configurations. The topology used is generally dependent on the particular communication protocol being implemented. For example, Token Ring utilizes a star-wired ring topology, while RS-485 requires a linear bus typology. Each topology has benefits and disadvantages.
A linear bus topology consists of a main run of cable onto which, devices, or nodes, are patched. Linear bus topology is easy to connect and may be more economical over some other topologies because of reduced cable lengths, when properly routed. However, a break in the main cable results in the failure of the entire network. Terminators are required at least at one end of the main cable in order to reduce reflection of electrical signals within the main cable. Generally, troubleshooting network issues can be difficult especially if the problem causes the entire network to fail. A linear bus topology is not meant to be implemented as a stand-alone solution for large networks.
A star topology is configured with each node connected directly to a central hub. The data is transmitted to the hub and then relayed to the destination. The hub provides control of all functions of the network and acts as a repeater for the data flow. The star topology is often seen in home offices and other small networks because of the ease of installation and troubleshooting, and no network disruptions when adding or removing devices. However, star topology has the added cost of a hub over the linear bus and while generally reliable, if the hub fails, all nodes attached to the hub are disabled.
Star-wired ring topology is generally only used in Token Ring networks. While star-wired ring networks may outwardly look like star networks, internally, the multistation access unit is wired to allow information to pass from device to device in a circle or ring.
Tree topology is best thought of as a hybrid between a linear bus topology having branches of star topology networks. Thus, a linear bus forms a backbone linking multiple star networks. This topology is most often seen in large network implementations where each star network forms a local group, perhaps defining a department within a company, these department-based networks are linked together to form the network infrastructure of the whole company. Tree topology shares the benefits and disadvantages of both linear bus and star topologies.
Due to the Ethernet protocol requirement that a signal transmitted on the network cable must reach every part of the network within a specified length of time, the tree topology is limited in the number of hubs it can implement. Each hub adds a small amount of lag to the transmission. Consequently, when designing a tree network, care is taken to ensure that between any two nodes on the network there exits no more than 5 segments and no more that 4 hubs are used.
A free-topology architecture allows wiring of devices with virtually no topological restrictions. However, by its very nature, free-topology is subject to variable line, i.e., network cable, loads as well as signal reflection caused by unterminated lines. Devices connected using free-topology must be able to handle these variable line loads and produce output, which is independent of the load. In addition, circuitry must be present to reduce reflection.
While the above discussion of various wiring topologies centered on network implementations, the same basic topologies apply to peripheral connectivity, i.e., connecting multiple devices, sensors, actuators, etc. to a central controller or monitoring device. Specifically, this is most often seen in security monitoring systems, which may include various sensors, actuator-driven locks, video cameras, and alarms of various types. These peripheral devices need to be wired to one or more monitoring stations. The monitoring stations receive signals from these peripheral devices, process the data, and provide some warning signal when necessary. In addition, such monitoring stations may transmit signals to the peripheral devices for setting operating parameters, requesting status updates, etc., as well. Consequently, quite a bit of data can flow between a monitoring station and the various peripheral devices.
Additionally, many security systems are installed after a building or home has been built. In this post-construction case, it is difficult and costly to run wiring needlessly. Thus as with the networking implementations, wiring topologies need to be selected that provide the necessary data bandwidth while still being cost-effective and efficient to install.
Security monitoring systems that are tied to one topology or another are less desirable, in that such a system may be perfectly suited for one installation scenario, and woefully ill-suited for the multiple other installation scenarios that may be encountered. Accordingly, it is desirable to have a security monitoring system that allows for a broad range of topologies—a free-topology based security monitoring system.